Biowaiver Monographs for Immediate Release Solid Oral Dosage Forms: Amitriptyline Hydrochloride

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1 COMMENTARY Biowaiver Monographs for Immediate Release Solid Oral Dosage Forms: Amitriptyline Hydrochloride R.H. MANZO, 1 M.E. OLIVERA, 1 G.L. AMIDON, 2 V.P. SHAH, 3 J.B. DRESSMAN, 4 D.M. BARENDS 5 1 Pharmacy Department, Chemical Sciences Faculty, National University of Córdoba, Córdoba, Argentina 2 College of Pharmacy, University of Michigan, Ann Arbor, Michigan 3 International Pharmaceutical Federation FIP, Den Haag, The Netherlands 4 Department of Pharmaceutical Technology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany 5 RIMV, National Institute for Public Health and the Environment, Bilthoven, The Netherlands Received 8 June 2005; accepted 7 February 2006 Published online in Wiley InterScience ( DOI /jps ABSTRACT: Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing amitriptyline hydrochloride are reviewed. Its therapeutic uses, its pharmacokinetic properties, the possibility of excipient interactions and reported BE/ bioavailability (BA) problems are also taken into consideration. Literature data indicates that amitriptyline hydrochloride is a highly permeable active pharmaceutical ingredient (API). Data on the solubility according to the current Biopharmaceutics Classification System (BCS) were not fully available and consequently amitriptyline hydrochloride could not be definitively assigned to either BCS Class I or BCS Class II. But all evidence taken together, a biowaiver can currently be recommended provided that IR tablets are formulated with excipients used in existing approved products and that the dissolution meets the criteria defined in the Guidances. ß 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95: , 2006 Keywords: amitriptyline hydrochloride; Biopharmaceutics Classification System (BCS); permeability; solubility; absorption; biowaiver INTRODUCTION This paper reflects the scientific opinion of the authors and not the policies of regulating agencies. Correspondence to: D.M. Barends (Telephone: þ ; Fax: þ ; dirk.barends@rivm.nl) Journal of Pharmaceutical Sciences, Vol. 95, (2006) ß 2006 Wiley-Liss, Inc. and the American Pharmacists Association A monograph based on literature data is presented on amitriptyline hydrochloride, with respect to its biopharmaceutical properties and the risk of waiving in vivo bioequivalence (BE) testing in the approval of new immediate release (IR) solid oral dosage forms containing this active pharmaceutical ingredient (API), including both reformulated products and new, multisource drug products. The purpose and scope of this series of monographs were discussed previously. 1 Briefly, the aims of the present study are to evaluate all pertinent data available from literature sources to assess the appropriateness of such a biowaiver from the biopharmaceutical point of view and also from the perspective of public health. The progress in this series can be followed at the FIP Website. 2 Up to now, monographs have been published on acetaminophen (paracetamol), 3 atenolol, 1 chloroquine, 4 ibuprofen, 5 propranolol, 1 ranitidine, 6 and verapamil JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006

2 BIOWAIVER MONOGRAPHS FOR AMITRIPTYLINE HYDROCHLORIDE 967 EXPERIMENTAL A search in the PubMed Central and Scirus was conducted using the keyword amitriptyline combined with: absolute, absorption, aqueous, bioavailability, permeability, pharmacokinetics, oral, and solubility. Whenever possible, original literature was consulted; data from secondary sources were included for completeness or when original literature could not be located. GENERAL CHARACTERISTICS Amitriptyline is an INN name. Its chemical name is 3-(10,11-dihydro-5H-dibenzo[a,d]cyclohepten- 5-ylidene)-propyldimethylamine. The molecular weight and melting point of amitriptyline hydrochloride are and C 8, respectively. Its structure is shown in Figure 1. Therapeutic Indication and Therapeutic Index The major therapeutic indication for amitriptyline is for the treatment of depression, although is also indicated for a number of nervous system related disorders. 9 In the treatment of depression, amitriptyline hydrochloride is given by mouth initially in a daily dose of 75 mg. Thereafter, the dose may be gradually increased, if necessary, to 150 mg daily. Therapy may also be begun with a single dose of mg, increased by 25 or 50 mg as necessary to a total of 150 mg daily. Doses of up to 200 mg daily and, occasionally, up to 300 mg daily have been used in severely depressed patients. 10 Severe symptoms of overdosage have been described, including unconsciousness, convulsions and myoclonus, hyperreflexia, hypothermia, hypotension, metabolic acidosis, and respiratory and cardiac depression, with life-threatening cardiac arrhythmias that may recur some days after apparent recovery. 10 No data are available on the dose that gave rise to these symptoms. CHEMICAL PROPERTIES Salts, Isomers, and Polymorphs In therapeutic use are an ester: amitriptyline embonate and the hydrochloride salt. This monograph will refer exclusively to amitriptyline hydrochloride. Polymorphic forms have not been reported, nor are there stereoisomers. Solubility Amitriptyline hydrochloride is soluble 1:1 in water. 11 The USP 12 and the Ph. Eur. 7 report this API to be freely soluble in water. Amitriptyline free base is practically insoluble in water and its solubility in 0.1 M sodium hydroxide at was recorded as mg/ml. 13 More recently, its solubility at 258C was measured, using both the acid-base titration method and the shake-flask method. 14 Both methods gave mg/ml. Experimental measured values of the solubility at 378C in different physiologically relevant phs, as required by the different Guidances, were not found, but solubilities at 258C were estimated from the solubility and pka. Taking the lowest reported solubility at that temperature, that is, mg/ml, and the pka value at 258C reported, that is, 9.45 (see below), the values of Table 1 were calculated, whereas the solubility in ph 1.2 was estimated from the solubility of 1:1, reported for amitriptyline hydrochloride. 11 Several reports indicate the protonated form of amitriptyline to self-aggregate with a critical micelle concentration of mol/l and an aggregation number of Figure 1. Structure of amitriptyline hydrochloride. Partition Coefficient Amitriptyline is a highly lipophilic molecule having a log P (octanol/water, ph 7.4) of 3.0, 11 while the intrinsic log P of the free base was reported as Calculations using fragmentation methods based on atomic contributions to lipophilicity gave values of 4.42 and 4.85, respectively. 22 Other workers reported a C log P of DOI /jps JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006

3 968 MANZO ET AL. Table 1. Calculated Solubilities of Amitriptyline Hydrochloride at 258C at Critical ph Values and Dose/Solubility Ratios for Different Tablet Strengths ph Calculated Solubility ph (mg/ml) Dose/Solubility Ratio (ml) for Different Tablet Strengths 10 mg 25 mg a 50 mg 75 mg 100 mg 150 mg b 416 b 555 b 832 b Solubilities at ph 7.5, ph 6.8, and ph 4.5 were calculated from the Henderson Hasselbalch equation: 43 SolutbilitypH ¼ 2:10 3 ð1 þð10 ph =10 9:45 ÞÞ in which and 9.45 are the solubility 14 and the pka of amitriptyline base, 14 respectively, both at 258. The solubility at ph 1.2 was estimated from the reported solubility of 1:1. 11 a WHO recommended dose. b Dose/solubility ratios higher than the critical value of 250 ml are indicated. pka The pka of amitriptyline has been reported as: ; 9.4 (248C 1), (258C), 14 and 9.31 (378C). 11 Available Strengths The WHO recommended dose is 25 mg. 25 IR solid dosage forms with marketing authorization (MA) in Argentina 26 and in Germany (DE) 27 have strengths of 10 mg up to 75 mg; in the USA, MAs have been given to tablet strengths up to150 mg. 28 Permeability The permeability in Caco-2 cell monolayers was measured at a high and a low concentration, in two directions. 23 Apparent Caco-2 permeability for apical to basolateral transport values reported for two concentrations were cm/s and cm/s, respectively. In the same study, the permeability of other APIs with a high fraction absorbed were also measured; all these APIs showed a permeability of approximately 10 5 cm/s or higher, indicating that amitriptyline is a high permeable API also. PHARMACOKINETIC PROPERTIES Absorption and BA Amitriptyline is passively absorbed 29 and undergoes extensive hepatic metabolism; it is metabolized in the liver to nortriptyline, an active metabolite that is also marketed separately. Amitriptyline and nortriptyline are distributed into the lungs, heart, brain, and liver. Both undergo enterohepatic circulation. Half-life values range from h for amitriptyline and h for nortriptyline. Pharmacokinetic determinations of both amitriptyline and nortriptyline show that the fraction absorbed from IR amitriptyline tablets is ,31 Although amitriptyline is well absorbed the oral BA is only 48% 11, 32 as a result of the extensive first-pass metabolism. The oral BA of an IR tablet versus an oral solution, expressed as AUC 1 was reported to be 112%. 33 DOSAGE FORM PERFORMANCE Excipients Excipients present in IR amitriptyline hydrochloride tablets with a MA in DE, Finland (FI), and The Netherlands (NL) are summarized in Table 2. In vivo comparisons of different formulations were not reported. Therapeutic inequivalence between brand-name drug products and FDA-approved generic drug products has not been reported 34 and there have been no reports of bioinequivalence of IR tablets with a MA in Argentina. 26 Dissolution The USP 28 specification for Amitriptyline Hydrochloride Tablets is not less than 75% (Q) dissolved JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006 DOI /jps

4 BIOWAIVER MONOGRAPHS FOR AMITRIPTYLINE HYDROCHLORIDE 969 Table 2. Excipients a Present in Amitriptyline Hydrochloride b IR Solid Oral Drug Products c with a Marketing Authorization (MA) in Germany (DE), Finland (FI), and The Netherlands (NL) Acacia DE (1) Aluminium hydroxide DE (2) Beeswax DE (1); NL (3, 4) Calcium carbonate DE (1); FI (5, 6) Calcium hydrogen phosphate DE (2, 7 10); NL (11) Calcium phosphate NL (3, 4) Calcium stearate DE (12) Carmellose sodium DE (13) Carnauba wax DE (1); FI (5, 6); NL (3, 4, 11) Cellulose DE (8, 10, 13 16); FI (17); NL (3, 4, 11, 18) Copovidone FI (17); NL (18) Croscarmellose DE (15) Croscarmellose sodium FI (17); NL (18) Crospovidone DE (16) Dibutyl phthlate NL (19) Diethyl phthlate NL (20) Disodium edetate NL (20) Ethylcellulose NL (20) Gelatin DE (12) Glucose, liquid DE (1) Glyceryl palmitostearate NL (3, 4, 19) Hydroxypropylcellulose NL (3, 4, 11) Hypromellose DE (2, 7 9, 14, 15); NL (3, 4, 11, 19) Lactose DE (1, 2, 7 9, 12 16); FI (5, 6, 17); NL (3, 11, 18 20) Macrogol DE (2, 7 9, 12 15); FI (5, 6, 17); NL (3, 4, 18, 19) Magnesium stearate DE (1, 2, 7 10, 13 16); FI (5, 6, 17); NL (3, 4, 11, 18 20) Maize starch DE (1, 2, 7 10, 12, 14); FI (5, 6, 17); NL (3, 4, 11, 18, 19) Maize starch, pregelatinised DE (13) Methylcellulose NL (20) Polymethacrylate DE (1, 13); NL (19) Povidone DE (1, 8, 10, 13); FI (5, 6); NL (3, 4, 19) Shellac DE (1); NL (3, 4) Silica DE (2, 7 9, 12, 13); FI (17); NL (11, 18, 20) Sodium benzoate FI (6) Sodium starch glycolate DE (1, 2, 7 9, 14); NL (3, 4, 19) Starch NL (20) Starch, pregelatinised NL (20) Stearic acid NL (11) Sucrose DE (1); FI (5, 6) Talc DE (1, 12 14); NL (3, 4, 11, 19) 1. Amitriptylin-neuraxpharm 1 10/-25/-50 Dragees. 2. Amitriptylin beta 1 10 Filmtabletten. 3. Amitriptylinehydrochloride 10 mg, tabletten (MA holder: Katwijk Farma). 4. Amitriptylinehydrochloride 25 mg, tabletten (MA holder: Katwijk Farma). 5. Triptyl 1 10 mg tabletti. 6. Triptyl 1 25/50 mg tabletti. 7. Amineurin 1 10/-25 Filmtabletten. 8. Amineurin 1 50 Filmtabletten. 9. Amitriptylin beta 1 25 Filmtabletten. 10. Amitriptylin CT 25/-75 mg Tabletten. 11. Tryptizol, tabletten 10/25/50/75 mg. 12. Amitriptylin-RPh 1 25 mg Filmtabletten. 13. Amitriptylin-neuraxpharm 1 75/-100 Filmtabletten. 14. Novoprotect 1 10/-25 mg Filmtabletten. 15. Saroten 1 Tabs 50 mg Filmtabletten. 16. Syneudon 1 50 Tabletten. 17. Saroten 10/25/50 mg tabletti, kalvopäällysteinen. 18. Sarotex 10/25, omhulde tabletten 10/25 mg. 19. Amitriptyline HCl Gf 25 mg, omhulde tabletten. 20. Amitriptyline HCl, tabletten 10 mg (MA holder: Pharmethica). Sources of data: DE: FI: NL: a Colourants are not included. b Drug products containing other APIs than Amitriptyline Hydrochloride are excluded. c Excluded are dosage forms that are swallowed by the patient in liquid form, such as oral solution. DOI /jps JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006

5 970 MANZO ET AL. in 45 min in 900 ml 0.1 N HCl using the basket at 100 rpm. 12 Results of comparative studies in vitro of different formulations were not reported. DISCUSSION Solubility The FDA defines highly soluble over the ph range 1 7.5; 15 while the EU 16 and the recently revised WHO Guidelines 17 limit the requirements to the ph range It was recently suggested that the FDA should also redefine the solubility boundaries for BCS Class I to ph At 258C, all tablet strengths conform to the criterion of 250 ml for the dose/solubility ratio at ph 6.8 and below, see Table 1. At ph 7.5, the WHO recommended dose complies with this dose/solubility ratio criterion but higher tablet strengths do not. However, these data refer to 258C, not at 378C, as required by the Guidances If amitriptyline hydrochloride, like most drug substances, has an endothermic heat of solution it is reasonable to assume that amitriptyline hydrochloride will exhibit higher solubility at 378C. On the other hand, calculating solubilties, using the Henderson Hasselbalch equation, are highly inaccurate and differences between the calculated solubility and the experimental value of up to a factor of 776 have been reported. 36 In summary, experimental solubility data at the conditions specified by the BCS Guidances are lacking and no concrete conclusion can be drawn as to whether amitriptyline hydrochloride meets either the FDA 15 or EU/WHO 16,17 definition of highly soluble. Permeability According to the present FDA and EU BCS Guidances, an API is classified as highly permeable if the fraction absorbed is 90% or higher 15,16 whereas the recently revised WHO Guidelines 17 sets a lower limit of 85% absorbed. Amtriptyline hydrochloride fulfills both criteria. Both log P and Caco-2 permeability data support the classification of this API as highly permeable. Surrogate Techniques for In Vivo BE Testing For amitriptyline hydrochloride, it is unlikely that bioinequivalence between two IR solid oral dosage forms would arise from differences in permeability produced by formulation differences, in view of its high and hence non-critical permeability. 37 Bioinequivalence between formulations, if any exists, would most probably be caused by differences in in vivo dissolution, which is expected to be the most critical parameter in the absorption process, at least in the neutral ph range. Consequently, for amitriptyline hydrochloride IR solid oral dosage forms, comparative in vitro dissolution testing as per BCS Guidances is an appropriate surrogate technique for in vivo BE testing. The dissolution test USP 28 for amitriptyline hydrochloride Tablets uses dilute hydrochloric acid as test medium. In view of the solubility characteristics of amitriptyline hydrochloride, this dissolution medium is likely to be less discriminating than testing at a ph of about 6.8. Risks with Respect to Excipient and/or Manufacturing Variations Table 2 shows that a wide variety of well-known excipients used in IR amitriptyline hydrochloride formulations with MAs in a number of countries. In contrast to some previously discussed APIs 3,5,6 the bioavailability committee of the regulatory authorities of DE classified amitriptyline hydrochloride in1998 as an API for which in vivo BE testing was required. 38 So, at least for the MA s granted in DE, it can be assumed that these drug products successfully passed an in vivo BE study versus the innovator s drug product. The lack of reports of BA/BE problems supports the view that these common excipients will have no effect on the BE of a test drug product, as long as they are incorporated in amounts currently used in IR tablet formulations. An indication of the amounts usually present in dosage forms for drug products with a MA in the USA can be obtained from the FDA Inactive Ingredients Database. 39 Risk of Bioinequivalence in Terms of Therapeutic Outcome The Argentine Health Authority classified amitriptyline hydrochloride as an intermediate health-riskdrug, 40 which means that eventual complications of the sickness and/or adverse reactions arising from plasma concentrations outside the therapeutic window of the drug are not necessarily serious, and are unlikely to compromise the integrity of the individuals or be life-threatening. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006 DOI /jps

6 BIOWAIVER MONOGRAPHS FOR AMITRIPTYLINE HYDROCHLORIDE 971 BCS Classification and Biowaiving Amitriptyline hydrochloride is highly permeable, but, as solid solubility data are lacking, no definitive conclusion can be drawn as to whether amitriptyline hydrochloride is highly soluble. Until appropriate experimental data are available, amitriptyline hydrochloride must be regarded as lying at the interface of BCS Class I/II. Other workers reached the same conclusion. 41 Still other workers classified amitriptyline hydrochloride as BCS Class I, but this classification was reached on the basis of calculated log P data, and took only the 25 mg tablet strength into account. 22,29,42 Nevertheless, all available data suggest that, even if a limited solubility of this API at ph 7.5 at 378C should exist, this will not be problematic in vivo because, owing to its high permeability, the major absorption occurs in the first portion of the small intestine where ph is below 7. Moreover, compararative in vitro dissolution testing at ph 6.8, as requested in the BCS Guidances, can be expected to detect any bioinequivalence caused by differences in in vivo dissolution. CONCLUSION Despite the relative uncertainty of the BCS classification for amitriptyline hydrochloride, a biowaiver is scientifically justifiable for this API, provided that the test product is formulated with the excipients shown in Table 2, in amounts currently used in IR tablet formulations 39 and shows rapid in vitro dissolution, according to the criteria as defined in the BCS Guidances ACKNOWLEDGMENTS Gert Ensing, RIVM, is acknowledged for aggregating the excipient information into tabular format. REFERENCES 1. Vogelpoel H, Welink J, Amidon GL, Junginger HE, Midha KK, Möller H, Olling M, Shah VP, Barends DM Biowaiver monographs for Immediate Release solid oral dosage forms based on Biopharmaceutics Classification System (BCS) literature data: Verapamil hydrochloride, propranolol hydrochloride, and atenolol. J Pharm Sci 93: page¼pharmacy_sciences&pharmacy_sciences¼ sciences_bioavail_groupbcs. 3. Kalantzi L, Reppas C, Dressman JB, Amidon G, Junginger HE, Midha KK, Shah VP, Stavchansky SA, Barends DM Biowaiver monographs for immediate release solid oral dosage forms: Acetaminophen (paracetamol). J Pharm Sci 95: Verbeeck RK, Junginger HE, Midha KK, Shah VP, Barends DM Biowaiver monographs for immediate release solid oral dosage forms based on biopharmaceutics classification system (BCS) literature data: Chloroquine phosphate, chloroquine sulfate and chloroquine hydrochloride. J Pharm Sci 94: Potthast H, Dressman JB, Junginger HE, Midha KK, Oeser H, Shah VP, Vogelpoel H, Barends DM Biowaiver monographs for immediate release solid oral dosage forms: Ibuprofen. J Pharm Sci 94: Kortejärvi H, Yliperttula M, Dressman JB, Junginger HE, Midha KK, Shah VP, Barends DM Biowaiver monographs for immediate release solid oral dosage forms: Ranitidine hydrochloride. J Pharm Sci 94: Ph. Eur. 5th edn Amitriptyline hydrochloride, monograph Strasbourg, France, Council of Europe. 8. The Merck Index Version 12.1 on CD-ROM. Merck & Co., Whitehouse Station, NJ, USA. 9. Clinical Pharmacology ß 2003, Gold Standard Multimedia Inc. http// 10. Martindale: The complete drug reference. Electronic version In: Sweetman S, editor, ed., London UK: Pharmaceutical Press, Thomson MICROMEDEX, Greenwood Village, Colorado. 11. The Pharmaceutical Codex Principles and practice of pharmaceutics, 12th edn. Pharmaceutical Press. 12. USP 28-NF The United States Pharmacopeia The National Formulary. Rockville MD. The United States Pharmacopeial Convention, Inc. 13. Green AL Ionization constants and water solubilities of some aminoalkylphenothiazine trankillizers and related compounds. J Pharm Pharmac 19: Avdeef A. Determination of drug solubility using a potentiometric acid-base titration method compared to the saturation shake-flask method: (after registration) 15. FDA Guidance for Industry: Waiver of in vivo bioavailability and bioequivalence studies for immediate-release solidoral dosage forms based on a Biopharmaceutics Classification System. US DOI /jps JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006

7 972 MANZO ET AL. Food and Drug Administration, Center for Drug Evaluation and Research. USA. gov/cder/guidance/3618fnl.pdf 16. CPMP Note for guidance on the investigation of bioavailability and bioequivalence WHO Multisource (generic) pharmaceutical products: Guidelines on registration requirements to establish interchangeability. Working document AS/04.093/Rev.4. World Health Organization. pharmprep/qas04_093rev4_final.pdf 18. Schreier S, Malheiros SVP, Paula E Surface active drugs: Self-association and interaction with membranes and surfactants. Physicochemical and biological aspects. Biochim Biophys Acta 1508: Nagappa AN, Kole PL, Pandi PV, Shanmukha I, Girish K, Mishra RPK Role of surface activity in mechanism of actions of tricyclic antidepressants. Colloids Surf B Biointerfaces 32: Kim EJ, Shah DO Cloud point phenomenon in amphiphilic drug solutions. Langmuir 18: Hansch C, Leo A, Hoekman D Exploring QSAR. Hydrophobic, electronic and steric constants. Washington, DC: American Chemical Society. 22. Kasim NA, Whitehouse M, Ramachandran C, Bermejo M, Lennernas H, Hussain AS, Junginger HE, Stavchansky SA, Midha KK, Shah VP, Amidon GL Molecular Properties of WHO Essential Drugs and Provisional Biopharmaceutical Classification. Mol Pharm 1: Faassen F, Vogel G, Spanings H, Vromansa H Caco-2 permeability, P-glycoprotein transport ratios and brain penetration of heterocyclic drugs. Int J Pharm 263: Blessel KW, Rudy BC, Senkowsky BZ In: Florey Analytical profiles of drug substances, Vol. 3. London, UK: Academic Press, pp WHO Essential medicines model list, 14th edn. pdf. 26. Administración Nacional de Medicamentos, Alimentos y Tecnología Médica de la República Argentina: Rote Liste 1 Service GmbH FMG Arzneimittelverzeichnis fur Deutschland. In Verlag EG, (after registration). 28. Elavil 1 Professional Information Brochure Elavil 1 (Amitriptyline HCl) Tablets and Injection: Varma MV, Sateesh K, Panchagnula R Functional role of P-glycoprotein in limiting intestinal absorption of drugs: Contribution of passive permeability to P-glycoprotein mediated efflux transport. Mol Pharm 2: Burch JE, Herries DG The demethylation of amitriptyline administered by oral and intramuscular routes. Psychopharmacology (Berlin) 80: Burch JE, Hullin RP Amitriptyline Pharmacokinetics: A crossover study with single doses of amitriptyline and nortriptyline. Psychopharmacology (Berlin) 74: Baldessarini RJ Fármacos y Tratamientos de los trastornos psiquiátricos. Depresión y manía. In Hardman JG, Limbrid LE, Molinoff PB, Ruddon RW, Goodman Gilman A, editors. The Pharmacological Basis of Therapeutics, 9th edn, Mexico: McGraw-Hill Co., pp Saroten 1 Tabs 50 mg Fachinformation Rote Liste 1 Service GmbH FMG. Arzneimittelverzeichnis fur Deutschland. In Verlag EG, editor. Aulendorf, Germany. (after registration). 34. The Medical Letter 1 on Drugs and Therapeutics (W 1141) October 14, pp The Medical Letter, Inc, NY. http// com/freedocs/gendrugs.pdf. 35. Yu LX, Amidon GL, Polli JE, Zhao H, Mehta MU, Conner DP, Shah VP, Lesko LJ, Chen ML, Lee VHL, Hussain AS Biopharmaceutics Classification System: The scientific basis for biowaiver extensions. Pharm Res 19: Bergström CA, Luthman K, Artursson P Accuracy of calculated ph-dependent aqueous drug solubility. Eur J Pharm Sci 22: Amidon GL, Lennernäs H, Shah VP, Crison JR A theoretical basis for a Biopharmaceutics Drug Classification: The correlation of in vitro drug product dissolution and in vivo bioavailability. Pharm Res 12: Gleiter GH, Klotz U, Kuhlmann J, Blume H, Stanislaus F, Harder S, Paulus H, Poethko-Muller C, Holz-Slomczyk M When are bioavailability studies required? A German Proposal. J Clin Pharmacol 38: U.S. Department of Health and Human Services Food and Drug Administration Center for Drug Evaluation and Research (CDER), Office of Generic Drugs, Division of Labeling and Program Support. The Inactive Ingredients Database. fda.gov/cder/iig/iigfaqweb.htm. 40. Administración Nacional de Medicamentos, Alimentos y Tecnología Médica de la República Argentina Disp. 3185/99: Requerimientos de Estudios de Bioequivalencia. gov.ar/normativa/normativa/medicamentos/disposición_anmat_ pdf. 41. Lindenberg M, Kopp S, Dressman JB Classification of orally administered drugs on the JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006 DOI /jps

8 BIOWAIVER MONOGRAPHS FOR AMITRIPTYLINE HYDROCHLORIDE 973 Word Health Organisation Model list of Essential Medicines according to the biopharmaceutics classification system. Eur J Pharm Biopharm 58: Wu CY, Benet LZ Predicting drug disposition via application of BCS: Transport/absorption/ elimination interplay and development of a biopharmaceutics drug disposition classification system. Pharm Res 22: Amidon GL Drug derivatization as a means of solubilization: Physicochemical and biochemical strategies. In: Samuel H. Yalkowsky, editors. Techniques of solubilization of drugs. New York: Marcel Dekker, Inc. DOI /jps JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 95, NO. 5, MAY 2006